1. Field of the Invention
The present invention relates to an image recording apparatus and an image recording method which record an image by ejecting ink droplets onto a sheet-like recording medium.
2. Description of the Background Art
A line head inkjet printer which records an image on printing paper by ejecting ink droplets from a plurality of nozzles arranged in a direction perpendicular to the transport direction of the printing paper while transporting the printing paper has been hitherto known. In the line head inkjet printer, it is necessary that the nozzles are arranged along substantially the full width of the printing paper. However, the use of a single elongated recording head requires the repair or replacement of the whole recording head in the event of a failure of one or some of the nozzles in the recording head. This is disadvantageous in production efficiency and in costs.
To solve such a problem, a head unit including a plurality of recording heads arranged in a staggered configuration along the width of printing paper has been hitherto used (as disclosed, for example, in Japanese Patent Application Laid-Open No. 2008-221547). The use of such a head unit requires the repair or replacement of only a failed recording head in the event of the failure of the recording head. This enhances the production efficiency and suppresses costs required for the repair and the like. However, the use of the plurality of recording heads gives rise to another problem in that unevenness in density is prone to result at a joint between adjacent ones of the recording heads.
Shading compensation has been hitherto known as a technique for suppressing unevenness in density at a joint between adjacent recording heads. The shading compensation is a technique which includes the steps of: reading a printed image with a scanner; converting the brightness values of the read image into print density values to produce a compensation table; and controlling the amount of ink ejected from the nozzles, based on the compensation table (as disclosed, for example, in Japanese Patent Application Laid-Open No. 2013-71289).
In an inkjet printer, there are cases where an undesirable flow and bleeding of ink occur pronouncedly depending on the type of printing medium and the type of ink. In such cases, unevenness in density sometimes occurs in a position deviated from a nozzle causative of the unevenness in density, rather than immediately under the causative nozzle. It is difficult for the shading compensation made in these cases to appropriately correct the causative nozzle because the position of the causative nozzle is different from the position where the unevenness in density occurs. Thus, there is a need for a technique capable of suppressing the unevenness in density as well as coping with an undesirable flow and bleeding of ink.
A technique which copes with an undesirable flow and bleeding of ink is disclosed, for example, in Japanese Patent Application Laid-Open No. 6-152902 (1994). To suppress the bleeding of ink between black ink and other-than-black color ink, the technique disclosed in Japanese Patent Application Laid-Open No. 6-152902 (1994) shows that black pixels and other-than-black color pixels which are positioned at the boundary between a black image portion and an other-than-black color image portion are recorded so that every other dot is skipped.
However, there has not yet been proposed any technique which copes with an undesirable flow and bleeding of ink between recording heads in a head unit including the recording heads arranged in a staggered configuration.